Ziegler-Natta (ZN) catalyst systems are well known for their capability to polymerize olefins. They in general consist of a support which mostly is magnesium based onto which titanium component has been added along with organic compound known as internal donor. This catalyst when combined with co-catalyst and/or external donor comprise of the complete ZN catalyst system.
Ziegler-Natta catalyst system which typically consists of transition metal halide normally titanium halide supported on metal compound which is typically magnesium dichloride. Along with transition metal, also there is organic component known as internal electron donor that plays a typical role during catalyst synthesis and polymerization. MgCl2 carrier, where the MgCl2 is in active form, can be created by various methodologies. One of the methods is precipitating the MgCl2 from an organic solution where magnesium is present as a soluble compound. The soluble magnesium compound can be achieved either by starting from Mg metal and treating it with a suitable alcohol in the presence of iodine, or starting from a magnesium alkyl and treating it with an alcohol. This step is then followed by chlorination of Mg alkyl or alkoxy compounds by a chlorination agent. The magnesium carrier can also be precipitated in the form of ‘ready-made’ MgCl2. In that case the MgCl2 has to be dissolved first in some suitable donor compound and then precipitated in hydrocarbon solvent. The MgCl2 support material can also be precipitated by chlorinating a soluble magnesium alkyl compound simply by treating it with chlorine gas or hydrochloric acid. Once the desired specification of carrier is obtained, this is generally followed by titanation procedure which finally results in the catalyst synthesis.
U.S. Pat. No. 4,277,589 of Montedison & Mitsui describes a process of solid catalyst based on magnesium ethanol adduct as the starting material followed by the addition of electron donor at 60° C. in halogenating agent. The resultant solid component is isolated and then treated with titanium compound at higher temperature and then filtered. The above step is repeated thrice afterwards hydrocarbon solvent. The magnesium ethanol complex has variation in ethanol complexation ranging from 2 to 6. The halogenating reagent that has been used is aluminum alkyl based.
U.S. Pat. Nos. 4,473,660, 4,156,063, 4,174,299, 4,226,741, 4,315,836 and 4,331,561 of Montedison describes a process magnesium chloride ethanol adduct has been halogenated using aluminum alkyls and then treatment with donor followed by titanium component to give solid catalyst. The variation in electron donor on polymerization is also disclosed.
U.S. Pat. No. 7,659,223B2 of Borealis describes the process for preparing olefin catalyst based on a liquid/liquid two phase system (emulsion) where no separate carrier materials are needed in order to get solid catalyst particles. The catalyst particles have predetermined size range and formed through solubilizing the magnesium higher alcohol complex and in situ generation of internal donor followed by addition of titanium, emulsifier and turbulence minimizing agent. Addition of alkyl aluminum is also done which provides the addition stability to the catalyst to work at higher temperatures. The produced catalyst has excellent morphology, good particle size distribution and activity maximum at higher temperature. One disadvantage of the in situ generation of internal donor is the variation in the composition of the internal donor.
U.S. Pat. No. 7,608,555 describes a process of synthesizing catalyst in a controlled manner leading to control over desired chemical composition and morphology. This is also based on emulsion methodology but here the dispersion phase is taken to be immiscible and inert with respect to the media for example perfluorinated organic solvents as dispersing phase. Although the advantage is indeed on the catalyst morphology and chemical composition control but it increases the number of steps for catalyst synthesis and in situ generation of internal donor leads to the variation in the composition of the internal donor.
U.S. Pat. No. 6,420,499 describes the process where the catalyst is synthesized without producing harmful byproducts such as titanium alkoxy trichloride or requires large amounts of titanation reagent as well as washing solvent. The resultant catalyst synthesized from large number of steps has good activity. There is usage of titanium less magnesium compound containing magnesium, halogen and alkoxy which is treated with organic chloride to in situ generate the internal donor followed by titanation. This process does not involve the usage of emulsifier but in situ generation of internal donor has the disadvantage of the variation in the composition of the internal donor.
U.S. Pat. No. 6,849,700 describes the process where magnesium alkoxide, carboxylic acid halide and titanium tetrahalide are obtained as dissolved reaction product and then are precipitated in an aromatic hydrocarbon and are settled by either adding an aliphatic hydrocarbon to the precipitated reaction mixture or by precipitating and settling the dissolved reaction product with a mixture of an aliphatic and an aromatic hydrocarbon. Here again disadvantage is the number of steps are involved in the washing of intermediate and final product.
U.S. Pat. No. 6,706,655 discloses the method of preparation of an olefin polymerization catalyst component where there is formation of a new polymerization catalyst component. In the process, magnesium dialkyl or dihalide or alkyl alkoxide is reacted with an alcohol and the reaction product is reacted with an unsaturated dicarboxylic acid dihalide and a titanium tetrahalide. The catalysts displays good activity and morphology when a polyhydric alcohol such as ethylene glycol. This process has the disadvantage of in situ generation of multiple new types of internal donors and involves large number of steps.
U.S. Pat. No. 7,026,265 discloses the process for the preparation olefin polymerization catalyst which consists of magnesium dihalide, titanium tetrahalide and a carboxylic acid ester, in which the precursors of its constituents are reacted in solution from which the component is precipitated. This precipitation is being supplemented by co-precipitation of one or more oligoesters of the carboxylic acid formed in a controlled manner. This new methodology leads to improved polymer morphology and product composition consistency.
U.S. Pat. No. 7,220,696 of Mitsui Chemicals discloses a process of synthesizing the catalyst system by reacting a solid adduct of magnesium halide with alcohol and an internal electron donor which is again reacted with the internal electron donor having two or more ether linkages and finally treated with titanium compound once or many times in divided portions while suspending in an inert hydrocarbon solvent. There are large numbers of steps involved in going from initial to final stage of catalyst synthesis.
U.S. Pat. No. 4,990,479 discloses the catalyst system comprising of magnesium, titanium and halogen and phthalate based internal donor along with organoaluminum compound and organosilicon compound containing a cyclopentyl group, cyclopentenyl group, cyclopentadienyl group or their derivative to produce polymers having high stereoregularity and narrow MWD. The catalyst synthesis involves the usage of magnesium halide and higher alcohol to form soluble adduct to which phthalic anhydride is added followed by titanium component. Hence there is the process of in situ internal donor generation. Further this is contacted with phthalate based organic compound before finally treating it again with titanium component. The two TiCl4 treatment steps wash away all the side products and after the final hydrocarbon wash, the catalyst exhibit composition having predominantly amorphous MgCl2. The main disadvantage is the large number of steps involved in catalyst synthesis.
U.S. Pat. No. 5,844,046 of Mitsui focuses on the use of external donors to achieve a broad MWD but it also describes the preparation of solid catalyst components. The catalyst synthesis involves the usage of magnesium halide and higher alcohol to form soluble adduct to which phthalic anhydride is added followed by titanium component. Further it is reacted with phthalate based internal donor followed by filtration of solid component under hot conditions which is again treated with titanium component. The final product is washed with hydrocarbon. The amorphous MgCl2 is generated through precipitation of the soluble magnesium chloride alcohol adduct through titanation. Also there is in situ internal donor generation step which gives variation in the composition of the internal donor.
Mitsui EP0125911B1 discloses the process of catalyst synthesis which involves the dissolving MgCl2 with 2-ethyl-hexanol (EHA) together with di-isobutylphthalate as internal donor and then precipitating it using ethyl aluminum sesquichloride leading to formation of amorphous MgCl2. The solid portion is treated with titanium component twice and then washed with hydrocarbon. This type of a catalyst synthesis requires a waste disposal system for the catalyst side product and a recirculation system for TiCl4 and a recirculation system for the wash hydrocarbons.
BASF U.S. Pat. No. 6,034,023 discloses a catalyst containing an aluminum oxide/silica support, titanium compound (TiCl4), magnesium compound, halogen and a carboxylic ester. The magnesium dialkyl is contacted with support in an inert solvent and then treated with a strong chlorinating agent to form amorphous MgCl2. This was followed by treatment with titanium compound and internal donor that is phthalate based. For the washing purpose, the chemical activation of catalyst is carried by using TiCl4 in toluene. This process involves large number of steps and also usage of titanium component during washing.
U.S. Pat. Nos. 5,658,840 and 5,296,431 both describes the similar catalyst synthesis process where the magnesium dialkyl is contacted with support in an inert solvent and then treated with a strong chlorinating agent to form amorphous MgCl2. Before the titanium compound is added, ethanol is added to reduce the reducing power of dialkyl magnesium. This was followed by treatment with titanium compound and internal donor that is phthalate based.
U.S. Pat. No. 5,296,431 discloses that the treatment of the resultant catalyst with butyl lithium before polymerization improves the fine generation.
U.S. Pat. No. 5,658,840 discloses another step to remove inert solvent from the catalyst through usage of first filtration and then applying a pressure difference at temperatures of not more than 100° C. to obtain free-flowing and storable catalysts having high productivity and stereospecificity.
U.S. Pat. No. 6,107,231 also disclose the similar methodology of synthesizing the catalyst as the above mentioned patents. Here also the dialkylmagnesium is first contacted with the support which is silica having spheriodal morphology and then chlorinated using HCl gas leading to formation of amorphous MgCl2. This was followed by treatment with titanium compound and internal donor that is phthalate based. For the washing purpose, the chemical activation of catalyst is carried by using TiCl4 in different solvent systems having different polarity. The teaching of this patent is the fact that usage of aromatic solvent during chemical activation gives catalyst systems which produce polymers having reduced xylene and chlorine content. These types of processes generally give high fines during polymerization which is the main disadvantage. Here in all the above patents, the internal donor is added along with the titanium component.
U.S. Pat. Nos. 4,946,816, 4,866,022, 4,988,656, 5,013,702, and 5,124,297 are describing the common processes for producing catalysts comprising of making soluble magnesium compound from a magnesium carboxylate or magnesium alkylcarbonate. Then precipitating magnesium in the presence of transition metal halide and an organosilane was followed by reprecipitating the solid components by the use of a mixed solution containing tetrahydrofuran. Finally, reacting the reprecipitated particles with transition metal compounds and internal electron donor compounds, to produce catalyst having good morphology. These processes have the disadvantage of having too many steps in the production of the catalyst.
U.S. Pat. No. 7,232,785 of ABB Lummus describes a process of catalyst synthesis which involves large number of steps. The invention describes a Ziegler-Natta PP catalyst based on silica carrier with quite high polymerisation activity. In the catalyst preparation a silica support is used, which is then treated with a hydrocarbon soluble organomagnesium compound (dialkylmagnesium in ether and heptane). The organomagnesium compound in the solid catalyst is further converted into MgCl2 by using HCl. After the treatment with ethanol, titanium compound followed by phthalate based internal donor is added. This is followed by filtration, washing and chemical activation by using titanium compound in aromatic solvent. Here an entirely different process for generation of MgCl2 is being followed.
U.S. Pat. No. 5,459,116 of Samsung discloses a catalyst synthesis process which involves the treatment of anhydrous magnesium chloride with higher alcohol to form soluble complex to which internal electron donor having hydroxyl and ester group is added. The resultant solution is then treated with titanium compound and then washed to remove impurities. The addition of new internal donors can also be done along with soluble organomagnesium compound. Such catalyst synthesis process has the disadvantage of involving large number of steps.
U.S. Pat. No. 6,034,025 describes the catalyst synthesis process where anhydrous magnesium chloride is treated with cyclic ether as internal electron donor along with mixture of lower alcohols to form soluble organomagnesium compound which is further treated with titanium tetrachloride. After separation of supernatant, titanation in toluene was done twice followed by washing. The variation in mixture of alcohol goes from lower alcohol to higher alcohol combinations. These processes are liable to have large number of steps in the production of the catalyst.
However, to overcome the above mention problem there is a need of a simple and economical process involving fewer number of steps for the purpose of synthesizing a catalyst for polymerization of olefins, wherein the catalyst system shows excellent polymerization activity and stereoregularity.